Polders in the world – some additions

By now, I know that there are polders in at least 104 countries, with a total surface area of at least 573,000 square kilometres. I assume that a few more countries might still be added.

Regarding the total surface area, I believe that in reality it will be considerably larger, as it is difficult to determine in many cases. As stated at the time, polders are generally located in the floodplains along rivers, in depressions in the landscape, and in coastal and delta areas. Three types of polders can be distinguished: 1) reclaimed low-lying land; 2) lands gained on the sea; 3) drained lakes. Besides the Netherlands, Bangladesh, China, Germany, Japan, the United States, and South Korea are countries with many polders. A summarised overview of the polders per continent is shown in the table below.

A characteristic of polders is that, without a water management system in the form of drainage and artificial discharge, combined with provisions for protection against flooding, these areas are unsuitable for habitation, agricultural exploitation, urban areas, etc. Drained lakes form the most striking example of this, since pumping out of excess water is necessary here directly from the start. In many polders, an irrigation system is also present alongside the required drainage system.

In my short contributions to Flevolands Geheugen, I have addressed a multitude of aspects of polders in the world. This primarily concerned their existence, the reasons for their construction, water management, flood protection, the impact of climate change and human intervention, land subsidence, and urbanization. In this summarised overview, I would like to follow up on that by focusing on a number of specific aspects that have particularly caught my attention.

First of all, the presence of polders in at least 104 countries. I think very few people have that in mind. The Netherlands is often cited as the polder country par excellence. In fact, with its 20,000 square kilometres of polders, it is a small player, albeit an important one. A striking example of this happened during the flooding in the New Orleans area caused by Hurricane Katrina in 2005. I heard at the time from the spokesperson of Rijkswaterstaat that twelve American television crews had come to the Netherlands to report on how water management and flood protection was organised and implemented.

A second point is, with the exception of the Netherlands, the completely inadequate flood protection, particularly for urban areas in polders. In most countries where polders exist, the level of flood protection often amounts to not more than a risk of failure of once in 100 years. Millions of people now live in this situation. When a flooding occurs, climate change is usually cited as the reason, rather than the result of human activity. Even if climate change were indeed the reason, in my opinion, this must be taken into account in the design standards and any subsequent adjustments thereto.

A third point is the underestimation of land subsidence compared to the effects of sea level rise or changes in river discharge. In many polders, land subsidence is occurring considerably faster than the effects of sea level rise or more extreme river discharges. It is therefore of great importance that, in such cases, the expected effects of land subsidence are properly taken into account in the designs and modifications of polders.

A fourth point is the lack of operation and maintenance. Worldwide, there is always a great deal of attention in politics and the press for new developments - the completion of a land reclamation project, a pumping station, or a dam - which is then called a success. It is only a true success if, five years after construction, it turns out that the water management system and the facilities for protection against flooding are being properly operated and maintained. If that goes well during the first five years, it often goes well in the years that follow as well, but ongoing care is of great importance.

These are just some reflections. I hope that the points mentioned will receive more attention in the future where they play a role, so that the hundreds of millions of people who now live in flood-prone areas will be better protected and run less risk of being involved in a disaster.